java-design-patterns/double-checked-locking/src/main/java/com/iluwatar/doublechecked/locking/App.java

package com.iluwatar.doublechecked.locking;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

/**
 * 
 * Double Checked Locking is a concurrency design pattern used to reduce the overhead of acquiring a
 * lock by first testing the locking criterion (the "lock hint") without actually acquiring the
 * lock. Only if the locking criterion check indicates that locking is required does the actual
 * locking logic proceed.
 * <p>
 * In {@link Inventory} we store the items with a given size. However, we do not store more items
 * than the inventory size. To address concurrent access problems we use double checked locking to
 * add item to inventory. In this method, the thread which gets the lock first adds the item.
 * 
 */
public class App {

  /**
   * Program entry point
   * 
   * @param args command line args
   */
  public static void main(String[] args) {
    final Inventory inventory = new Inventory(1000);
    ExecutorService executorService = Executors.newFixedThreadPool(3);
    for (int i = 0; i < 3; i++) {
      executorService.execute(() -> {
        while (inventory.addItem(new Item()));
      });
    }

    executorService.shutdown();
    try {
      executorService.awaitTermination(5, TimeUnit.SECONDS);
    } catch (InterruptedException e) {
      System.out.println("Error waiting for ExecutorService shutdown");
    }
  }
}